This talk will look at an underdiscussed challenge to Radical Interpretation (construed as a metaphysical story about the foundations of intentionality). The challenge is mentioned in passing in Lewis’s “New work for a theory of universals” and recently re-presented by Brian Weatherson. The upshot threatens to be this: if two possibilities are evidentially and agentially the same for a subject, then the subject cannot represent the difference between the two. But many pairs of possibilities we do distinguish may satisfy the antecedent: sceptical and non-sceptical scenarios, roughly. I compare this to Berkeley’s representational scepticism, and explore what sort of responses are open to the radical interpreter.